1. Field of the Invention
The present invention relates to control systems and methods, and in particular, treatment systems, such as a water treatment plant and methods of operating the same.
2. Background of the Related Art
Water quality is something most Americans take for granted. The public""s first impression of water is aesthetically driven and is primarily determined by the visual quality of the water. Visual quality is a function of the amount of particles and color in water. Particles are finely divided solids from weathering processes and biological activity (clays, algae, bacteria, and other higher organisms) that are larger than molecules but generally not distinguishable by the naked eye. Standard methods for measuring and reporting visual quality use Turbidity and Particle Counts. Turbidity is an optical property of a sample causing light to be scattered and absorbed but not transmitted. The unit of measurement is Nephelometric Turbidity Units (NTU). Turbidity interferes with disinfection. The size, shape and refractive index of the particles suspended in the water affect the water""s light-scattering properties, thus making it difficult to correlate turbidity with the concentration of particles in the water. However, the particle size distribution can be established using particle counts.
In 1993, Milwaukee, Wis. reported a sharp increase in the number of incidents of diarrhea patients caused by Cryptosporidium. Investigations revealed that the Howard Water Treatment Plant was responsible for the outbreak. Historically, the Howard Water Treatment Plant consistently produced treated water with turbidities of less than 0.1 Nephelometric Turbidity Unit (NTU). However, during the time of the incident, the finished water turbidity levels ranged from 0.1 to 1.7 NTU while the influent turbidity was normal. During this period, the effluent samples always met the Wisconsin Department of Natural Resources""s regulations for turbidity.
Investigation by the Environmental Protection Agency showed that the Howard Water Treatment Plant personnel responded to turbidity changes by adjusting coagulant levels continuously to meet the demands of raw water quality (turbidity, taste, and odor). However, the dosage adjustments were not fast enough or optimum for the varying influent water quality. When the dosages reached an optimum level, the effluent turbidity came within control, demonstrating that the plant could produce low turbidity water under optimal chemical conditions. Accordingly, a system and method are needed that can predict improved or optimum chemical dosages in real time based upon influent water quality could reduce the response time or delay that can cause such incidents.
Thus, a need exists for a system and method to assure an adequate coagulant dose to reduce the influent turbidity by correlating treatment (e.g., coagulant) to turbidity.
Given the nature of the problem, it is almost essential to prevent turbidity. Breakthrough needs to be prevented rather than compensating for a monitored parameter, turbidity, or the like, breakthrough after occurrence. Parameters of secondary importance such as cost also need coordinated effective control. Given the economics, a system and method are needed to control or to optimize treatment to get maintain effective continuous effluent turbidity at a reduced or lowest chemical cost for real time process variables.
The Surface Water Treatment Rule (SWTR) establishes goals for filtration and disinfection for all surface water sources or groundwater sources under the direct influence of surface water. The SWTR and Enhanced Surface Water Treatment Rule (ESWTR) set forth criteria for treated water turbidity, disinfectant dosage, contact time, percent reduction or inactivation of Giardia cysts and enteric viruses, and monitoring requirements for Turbidity, Residual Disinfectant and percent removal of cysts.
The Surface Water Treatment Rule Guidance Manual specifies that the minimum finished water turbidities should not exceed 0.5 NTU in 95% of the samples taken every month. Because of the association of turbidity with pathogens that are difficult to disinfect like Giardia and Cryptosporidium, the Environmental Protection Agency (EPA) recommends that the filtered water turbidity before disinfection should be less than 0.1 NTU on a continuous basis. This provides greater confidence that pathogens are removed before disinfection, the last barrier in the treatment plant.
However, the Disinfectant and Disinfection Byproducts (D-DBP) Rule was introduced to regulate human carcinogenic compounds like Trihalomethanes and Haloacetic acid.
The primary purpose of Safe Drinking Water Act (SDWA) is to authorize federal oversight of public water supplies safety. SDWA gives USEPA broad authority to publish maximum contaminant level goals (MCLGs) and National Primary Drinking Water Regulations (NPDWRs) for drinking water contaminants. SDWA modifications require USEPA to publish an MCLG and promulgate an NPDWR for any contaminant that has an adverse effect on human health and is known to occur or has a substantial likelihood of occurring in public water systems at a frequency and at concentrations of public health concerns.
MSLGs are nonenforceable, health based goals. They represent a level at which there is no known or anticipated health effect on human health without regard to the cost of reaching these goals. Maximum Contaminant levels are the enforceable goals. They are set as close to the MCLG as feasible taking into account the best technology, treatment techniques, and other available means (taking cost into consideration).
The provisions of SDWA could increase the amount of regulated substances. Some of these newly regulated substances may require improved treatment techniques or a more complex treatment. Further, the SWTR, ESWTR and D-DBP set targets for removal or percent reduction of contaminants. These requirements may force the water treatment plants to improve the current operations or add new facilities to comply with the rules. Monitoring and reporting requirements under these rules are stringent to enforce compliance with the rules at all times.
In addition, the requirements under the different rules may conflict or lead to inherent violation. For example, SWTR disinfection requirements may force a water utility to maintain a higher disinfectant level, but this may cause violation of the D-DBP Rule requirements. Operators of water treatment plants have to continuously meet the requirements under several different rules simultaneously while operating the plant in a cost-effective manner. This task becomes especially challenging under rapidly varying raw water conditions. A real time control system and method is needed to provide the quick and optimal response that is necessary to ensure public safety and compliance with regulations.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the present invention is to provide an effluent control system and method that substantially obviates one or more of the above-described problems caused by limitations of the related art.
Another object of the present invention is to provide a real time control system and method for prediction and control of unit operations in an effluent treatment plant.
Yet another object of the present invention is to provide a treatment system and method for controlling all effluent quality parameters for unit operations in a effluent treatment plant.
Still yet another object of the present invention is to provide a water treatment system and method that predicts turbidity in unit operations of a water treatment facility.
A further object of the present invention is to provide a water treatment system and method that controls a dependent parameter based on independent parameters for a water treatment facility.
A further object of the present invention is to provide a water treatment system and method for controlling turbidity based on water quality and chemical dosage parameters.
A further object of the present invention is to provide a nonlinear predictive water control system and method for a selected water quality parameter that does not detrimentally effect remaining water quality parameters.
A further object of the present invention is to provide a control system and method that reduces chemical additions to a process while maintaining treated effluent requirement, in an effluent treatment plant.
A further object of the present invention is to provide a control system and method that constructs virtual sensors for parameters that can not be detected in-line in an industrial treatment plant.
A still further object of the present invention is to provide a water treatment system and method using neural networks, genetic algorithms and deterministic models to control water treatment plants and predict values of parameters within the treatment plant.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.